Modern commercial aircraft are designed to utilize the maximum available cabin space allocation to useable passenger payload capacity. Amenities for passengers are taken into consideration in the accommodation of the passengers. Such accommodations in the main cabin command a premium fare with regard to the space allocated and not available for passenger seating. The passenger aircraft fuselage containing the passenger main cabin is circular or ovoid in cross-section. The main cabin floor is typically located below the geometric center of the cross-section, allowing for the provision of a large passenger compartment. This arrangement provides for a ceiling, overhead stowage compartments and other amenities to serve the needs for the passengers and the passenger compartments. To maximize the passenger utilization and to optimize the revenue generated by the maximization of passenger seating capacity while providing a larger, attractive passenger cabin with appeal and comfort to the passengers, only those encumbrances directly attributable to the passengers benefit are provided, such as galleys, lavatories, closets and facilities directly related to these types of units.
The space above the overhead stowage compartments and ceiling includes ducts, cables, electrical and electronics equipment and other components. In general, the available space above the ceiling and overhead stowage compartments is significantly smaller than the passenger cabin itself. The space below the cabin floor is typically allocated for providing compartments essential for the aircraft operation, such as electrical equipment bays, water supply and wastewater stowage, in addition to cargo compartments for passenger baggage and revenue cargo. This below floor space usually is confined to the remainder of the cross-section available and is typically smaller in height and width than the main passenger cabin.
Long range, subsonic airliners are utilized on routes that are non-stop for duration of twelve hours or longer. For such a flight, federal regulations require the provision of pilot rest accommodations. For these same long duration flights, attendant rests are typically provided as well. A case in point is the Boeing 747™ airliner in which a small attendant rest accommodation is provided. This specific crew rest accommodation is positioned behind the passenger seating in the upper deck of a dual passenger seating deck aircraft. In another instance, for long distance flights the use of dedicated seats for pilots or other crew and changing spaces for the same is provided on the main deck. Additional use of space for specialized functions, including the cabin crew purser, is provided to serve passengers, which requires the allocation of workspaces on the main deck as well.